ABUJA (Reuters) - Nigerian President Goodluck Jonathan showed the power of incumbency on Saturday, mustering the support of more than two thirds of powerful state governors for the launch of his re-election campaign.

Thousands of cheering supporters gathered in Abuja's central Eagle Square to hear Jonathan proclaim his candidacy for the January election, shaping up to be the most fiercely contested since the end of military rule.

"Our country is at the threshold of a new era, an era that beckons for a new kind of leadership, a leadership that is uncontaminated by the prejudices of the past," said Jonathan, in his trademark fedora and traditional kaftan-like attire.

He listed ending power shortages, improving health and education and ensuring food self-sufficiency among his priorities. He also pledged to better manage oil revenues with a planned sovereign wealth fund and told kidnappers and criminals "that give us a bad name" to be ready for battle.

The election bid by Jonathan, from the oil-producing Niger Delta in the south, faces resistance from some parts of the north as it breaks an unwritten agreement that power should rotate between the country's main regions every two terms.

But analysts predicted Jonathan would only announce his candidacy if he was sure of winning enough support from within the ruling party. Saturday's rally seemed to demonstrate he had built up that confidence over recent weeks.

"The northeast zone will rally round you and we assure you that we will deliver you the highest number of votes come 2011," Isa Yuguda, governor of northeastern Bauchi state and once seen as a potential presidential contender, told the rally.

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Jonathan inherited the presidency when president Umaru Yar'Adua, a northerner, died this year during his first term, and some powerbrokers in the ruling People's Democratic Party (PDP) have said the next leader must be a northerner.

Key to Jonathan's fortunes at the mid-October primaries will be the state governors, who form a powerful caucus within the PDP. Twenty-six of the country's 36 governors, including several northerners, spoke at Jonathan's rally in support of his bid.

But three of them were also at the Eagle Square parade ground on Wednesday when former military ruler Ibrahim Babangida launched his rival campaign, and it would have been political suicide for the governors not to attend Saturday's rally.

"Nigerian politics has a Byzantine quality that makes it hard entirely to be sure it's over until it's over," said Antony Goldman, Nigeria expert and head of London-based PM Consulting.

"Jonathan is the front-runner. Northern rivals might hope to deny him more than 50 percent of delegates and take the primary to a run-off, but as things stand that would be quite an achievement," he said.

LOBBYING AHEAD

The PDP nominee has won all three presidential races since the end of military rule in 1999, making the outcome of past elections a foregone conclusion and bringing Africa's most populous nation close to being a one-party state.

But the presidential race this time is more contentious, with no consensus PDP candidate and no obvious "godfather" -- the powerful background figures who have in the past hand-picked the nominee -- holding sway over the party.

"In the next month the lobbying by all sides of hesitating governors and others of influence is likely to be intense," PM Consulting's Goldman said.

Babangida, a northerner who seized power in the OPEC member in August 1985 and ruled for nearly eight years, also wants the PDP ticket and is hoping northerners opposed to Jonathan will rally behind him. He has vowed he would serve only one term.

But Babangida too is a divisive figure. He was forced from power after cancelling an election that was generally regarded as fair, and this colors his political reputation.

He faces other northern challengers within the PDP including former vice president Atiku Abubakar, who switched to the ruling party after running unsuccessfully for president as the opposition Action Congress candidate in the last vote in 2007.

Kwara state governor Bukola Saraki and national security adviser Aliyu Gusau could also win northern backing if they decide to seek the PDP nomination, analysts say.

The threat to Jonathan from the northern factions depends on their ability to unite behind a single candidate. Should Babangida, Abubakar, Saraki and Gusau all push their campaigns to the finish line, they may fail to do so.